A truck is moving at a speed of 80 km / h; a passenger car is moving towards a meeting at a speed of 100

| August 10, 2021 | education

A truck is moving at a speed of 80 km / h; a passenger car is moving towards a meeting at a speed of 100 km / h, which is equal to the speed of a car relative to a truck.

Vg = 80 km / h.

Vl = 100 km / h.

Vlg -?

According to the law of relativity of speeds, the speed of a body relative to a stationary frame of reference Vн is the vector sum of the speed of a moving frame of reference relative to a stationary Vпн and the speed of a body relative to a moving frame of reference Vп: Vн = Vпн + Vп.

The fixed frame of reference is the earth, the movable frame of reference is the truck.

Therefore, the speed of the truck relative to the ground Vg, is the speed of the moving frame of reference relative to the stationary Vnp: Vnp = Vg.

The speed of a passenger car Vl, is the speed of the body, relative to the stationary frame of reference Vn: Vn = Vl.

The speed of a passenger car relative to the cargo Vlg is the speed of the body relative to the moving frame of reference Vp: Vlg = Vp.

Vl = Vg + Vlg.

Vlg = Vl – Vg – vector.

Let’s draw the OX coordinate axis in the direction of movement of the car.

Vlg = Vl – (- Vg) = Vl + Vg.

Vlg = 100 km / h + 80 km / h = 180 km / h.

Answer: the speed of a car relative to a truck is Vlg = 180 km / h.



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